Gold is the most noble of metals. In its pure state it is resistant to corrosion, a symbol of eternity, the colour of the sun.
Water gilding is a process that has remained unchanged for centuries. Linen is glued to the surface of an oak panel, which is then overlaid with layers of gesso (chalk and animal glue). When dry, the gesso is sanded until perfectly smooth. The design is engraved and carved, with additional gesso applied to create raised areas.
Areas to be gilded are then sealed with bole (clay mixed with animal glue). The remaining white gesso is the base for the egg tempera. Small sheets of gold are picked up with broad flat brushes and laid onto the bole surface wetted with a mixture of water, animal glue and alcohol. When dry the gilded surface can be rubbed with an agate stone, a burnisher, which compresses the surface and brings out the brilliance of the gold.
Modern materials are unable to replicate the subtlety and versatility of this ancient process.